Anguillosyllis dalgleishae, Neal & Drennan & Wiklund & Stewart & Rabone & Dahlgren & Glover, 2025

Neal, Lenka, Drennan, Regan, Wiklund, Helena, Stewart, Eva C. D., Rabone, Muriel, Dahlgren, Thomas G. & Glover, Adrian G., 2025, New species of Anguillosyllis Day, 1963 (Annelida, Syllidae) from polymetallic nodule exploration areas, eastern Clarion-Clipperton Zone, central Pacific Ocean, European Journal of Taxonomy 1026, pp. 30-64 : 40-47

Anguillosyllis dalgleishae sp. nov.

urn:lsid:zoobank.org:act:

Figs 3–5, 6A

Diagnosis

Body with 10 chaetigers. Prostomium in two parts, with three short antennae. Palps elongated, fused for at most ⅓–⅔ of their length. Parapodia with large conical dorsal lobes (flaps). Dorsal cirri on chaetiger 1 only. Heterogomph chaetae unidentate.

Etymology

The species name is dedicated to Claire Dalgleish, benthic operations lead on all cruises to the NORI-D area (C5a, C5d, C7a, C7b).

Material examined

Holotype

PACIFIC OCEAN – Eastern Central Pacific , Clarion Clipperton Fracture Zone • 12.0415° N, 117.2171667° W; 4094 m depth; 13 Mar. 2015; A.G. Glover, H. Wiklund, T. Dahlgren and M. Brasier leg.; Brenke Epibenthic Sledge; specimen GUID: 7195bc27-fb46-4f87-8c76-48266394b848; field ID; NHM_01867; GenBank 16S gene: PV579018; NHMUK ANEA 2024.2695 .

Paratypes

PACIFIC OCEAN – Eastern Central Pacific , Clarion Clipperton Fracture Zone • 1 spec.; 12.37098333 ° N, 116.61365° W; 4160 m depth; 21 Feb. 2015; A.G. Glover, H. Wiklund, T. Dahlgren and M. Brasier leg.; USNEL Box Core; specimen GUID: 42eab9a3-1d5c-43ec-86e2-4f5aa47bd5f1; field ID NHM_00837; GenBank 16S gene: PV579009; NHMUK ANEA 2024.2686 • 1 spec.; 12.25733333 ° N, 117.3021667° W; 4302 m depth; 1 Mar. 2015; A.G. Glover, H. Wiklund, T. Dahlgren and M. Brasier leg.; Brenke Epibenthic Sledge; specimen GUID: 4be32c49-79e4-4cb1-a7b2-12b6265ff348; field ID NHM_01347A; GenBank COI gene: PV577541; 16S gene: PV579012; NHMUK ANEA 2024.2689 • 1 spec.; 12.3635 ° N, 116.681° W; 4233 m depth; 10 Mar. 2015; A.G. Glover, H. Wiklund, T. Dahlgren and M. Brasier leg.; Brenke Epibenthic Sledge; specimen GUID: b6584f26-950c-4506-b7e0-aec9cd37c46e; field ID NHM_01669A; GenBank 16S gene: PV579019; NHMUK ANEA 2024.2697 .

Other material

PACIFIC OCEAN – Eastern Central Pacific , Clarion Clipperton Fracture Zone • 1 spec.; 12.13366667 ° N, 117.292° W; 4122 m depth; 24 Feb. 2015; A.G. Glover, H. Wiklund, T. Dahlgren and M. Brasier leg.; Brenke Epibenthic Sledge; specimen GUID: d5d9b8f4-8717-43e7-9e6f- 422ce4acfdb6; field ID NHM_01021; GenBank 16S gene: PV579010; NHMUK ANEA 2024.2687 • 1 spec.; 12.00945 ° N, 117.1781167° W; 4144 m depth; 27 Feb. 2015; A.G. Glover, H. Wiklund, T. Dahlgren and M. Brasier leg.; USNEL Box Core ; specimen GUID: 889e12a1-6e88-4987-9e8a- 1d758fd43ea3; field ID NHM_01201; GenBank 16S gene: PV579011; NHMUK ANEA 2024.2688 • 1 spec.; 12.45178333 ° N, 116.5122667° W; 4196 m depth; 4 Mar. 2015; A.G. Glover, H. Wiklund, T. Dahlgren and M. Brasier leg.; USNEL Box Core ; specimen GUID: 502bcd95-9ec8-4ed2-acea- e630ede84474; field ID NHM_01508C; GenBank COI gene: PV577525; 16S gene: PV579013; NHMUK ANEA 2024.2690 • 1 spec.; 12.52121667 ° N, 116.69815° W; 4237 m depth; 8 Mar. 2015; A.G. Glover, H. Wiklund, T. Dahlgren and M. Brasier leg.; USNEL Box Core ; specimen GUID: f4490e8c-6091- 4f27-85df-982e78912412; field ID NHM_01597; GenBank 16S gene: PV579014; NHMUK ANEA 2024.2691 • 1 spec.; 12.3635 ° N, 116.681° W; 4233 m depth; 10 Mar. 2015; A.G. Glover, H. Wiklund, T. Dahlgren and M. Brasier leg.; Brenke Epibenthic Sledge; specimen GUID: e40b2e1f-f476-4085- 9993-6dcf1221d8ad; field ID NHM_01657; GenBank 16S gene: PV579015; NHMUK ANEA 2024.2692 • 1 spec.; 12.17383333 ° N, 117.1928333° W; 4045 m depth; 11 Mar. 2015; A.G. Glover, H. Wiklund, T.vDahlgren and M. Brasier leg.; Brenke Epibenthic Sledge; specimen GUID: 589cb9f8-292c-4668- 940d-b2891384e4c0; field ID NHM_01773; GenBank 16S gene: PV579016; NHMUK ANEA 2024.2693 • 1 spec.; 12.17383333 ° N, 117.1928333° W; 4045 m depth; 11 Mar. 2015; A.G. Glover, H. Wiklund, T. Dahlgren and M. Brasier leg.; Brenke Epibenthic Sledge; specimen GUID: fb1eb56d-569c-4f11-83d0- 8c60ced37856; field ID NHM_01773A; GenBank 16S gene: PV579017; NHMUK ANEA 2024.2694 • 1 spec.; 12.00931667 ° vN, 117.3803° W; 4141 m depth; 15 Mar. 2015; A.G. Glover, H. Wiklund, T. Dahlgren and M. Brasier leg.; USNEL Box Core ; specimen GUID: d6d4cdd0-e6ab-4e61-b9b0- e2eb3881e64a; field ID NHM_01990; GenBank 16S gene: PV664892; NHMUK ANEA 2024.2696 • 1 spec.; 13.93242102 ° N, 116.5110797° W; 4143.62 m depth; 5 Mar. 2020; A.G. Glover, H. Wiklund, G. Bribiesca Contreras and E. Simon Lledó leg.; USNEL Box Core; specimen GUID: 9f76d801-e1bb- 42d2-830d-0caec6103f72; field ID NHM_04729_ ESDS5 ; GenBank 18S gene: PV579029; NHMUK ANEA 2024.2698 • 1 spec.; 12.37908954 ° N, 116.5576715° W; 4196.02 m depth; 11 Mar. 2020; A.G. Glover, H. Wiklund, G. Bribiesca Contreras and E. Simon Lledó leg.; USNEL Box Core; specimen GUID: 2cb21b0d-bbf1-4c9e-a04e-728c72a9041d; field ID NHM_04731_ ECDS2 ; GenBank 16S gene: PV579020; NHMUK ANEA 2024.2699 .

Description

MEASUREMENTS AND APPEARANCE. Relatively large sized species, up to 3.25 mm in length for 10 chaetigers ( Fig. 3B–C). Holotype NHMUK ANEA 2024.2695, posteriorly complete, 3.25 mm long and 0.45 mm wide at widest point for 10 chaetigers; right parapodia 9–10 removed for tissue sampling for DNA analysis. Paratype NHMUK ANEA 2024.2689, posteriorly complete, 2 mm long and 0.3 mm wide for 10 chaetigers, pygidial cirri missing, two left parapodia removed for tissue sampling for DNA analysis. Paratype NHMUK ANEA 2024.2697, posteriorly complete, 3 mm long and 0.4 mm wide for 10 chaetigers, pygidial cirri missing, three left parapodia removed for tissue sampling for DNA analysis. Paratype NHMUK ANEA 2024.2686, SEM specimen on stub ( Fig. 4A–G), posteriorly incomplete and damaged, ~ 2 mm long and 0.3 mm wide for about 8 chaetigers. Other specimens in variable condition due to preservation or tissue sampling for DNA analysis; five specimens posteriorly complete with 10 chaetigers, ranging in length from 2 mm to 3 mm and up to 0.4 mm at widest point. Body relatively straight, tapering only at the first segment anteriorly, and from the pygidium posteriorly. Live specimen semi-translucent, without pigmentation ( Fig. 3A); fixed specimen opaque, creamy white in ethanol ( Fig. 3B–C).

PROSTOMIUM. Rounded, slightly wider than long under light microscope ( Figs 3D, 5 A-inset); SEM shows differentiation into median quadrate lobe with deep notch on the posterior margin superimposed onto inferior rounded lobe ( Figs 4A–B, 6A). Eyes absent. Prostomium bearing three short, digitiform antennae and two palps ( Figs 3D–F, 4A–B, 5 A-inset). Antennae just under the length of the prostomium, with the median antenna slightly longer than lateral antennae and inserted posterio-dorsally on the prostomium; lateral antennae inserted more anteriorly. Palps smooth, somewhat elongate, approximately 1½ the length of the prostomium, and conical to somewhat finger-like in shape; palps sharply arcing ventrally from the base in almost all specimens and fused for at most ½–⅔ their length (degree of fusion not particularly clear) with distinct midline furrow and acute distal notch.

TENTACULAR SEGMENT. Achaetous, bearing two short ovate tentacular cirri, approximately ½ the length of the antennae and inserted laterally ( Fig. 5A). Pharyngeal tube extending to chaetigers 2–3; proventricle spanning from chaetigers 2–4, barrel to lightbulb-shaped, tapered posteriorly, with possibly ~ 15–20 muscle cell rows, though this is difficult to discern through body wall of preserved specimens ( Fig. 3B– C) and best observed in live specimen ( Fig. 3A). Partially everted pharynx observed in only one specimen ( Fig. 3G).

PARAPODIA. Somewhat short, rounded rectangular, and uniramous, with posterior-most two chaetigers somewhat thinner than on previous segments. Parapodia with large conical dorsal lobe ( Figs 4C, 5C) and two short, papilliform lobes ( Fig. 5A–C); posterior lobes smaller than anterior lobes on anterior-most chaetigers ( Fig. 5C), but developed moving posteriorly, becoming subequal in length to the anterior lobe around chaetiger 6, and slightly exceeding the anterior lobe in size on subsequent chaetigers. Dorsal cirri present only on chaetiger 1, where long, filiform ( Figs 3D–F, 4A–B, 5 A-insert); absent in other chaetigers. Ventral cirri short and conical with an expanded base, inserted midway along the parapodia ( Figs 3H, 5A–B). Several pointed acicula per parapodium visible, with tips non emergent ( Fig. 5E, marked by arrow). Each parapodium bearing dense bundles of numerous compound heterogomph chaetae, bundles becoming slightly sparser moving posteriorly, chaetae falcigerous to spiniger-like ( Fig. 4F–G). Falcigerous chaetae of chaetigers 1–4 with denticulated shafts, with denticles arranged in irregular horizontal rows ( Fig. 4D), from chaetiger 5 with shafts indistinctly denticulated or smooth ( Fig. 4E). Blades finely serrated, unidentate decreasing in length dorso-ventrally, ranging from elongate, slender spiniger-like to shorter falcigers ( Figs 4F–G, 5D), with blades of the longest spiniger-like chaetae 230–250 µm, and shortest falcigers 25–30 µm; chaetae emerge from semicircular flap that extends from posterior lobe ventrally towards the base of the parapodium.

PYGIDIUM. Conical to rounded; with four appendages; lateral cirri missing, ventromedial often missing, when present long, curled and filiform ( Fig. 3I).

Reproductive information

Three specimens ovigerous; eggs visible through body cavity wall in all specimens between chaetigers 6–10, eggs irregularly shaped, ~50 µm in diameter ( Figs 3A, 5F).

Genetic data

Specimens (n = 14) assigned to A. dalgleishae sp. nov. form a clade (Supp. file 3: Fig. S1, Supp. file 4: Fig. S2), with low intraspecific divergence across all sequences (maximum intraspecific p-distance/ K2P 0.5/0.5% for 16S and 1.3/1.3% for COI). Sequences matched with high % identity (99.7–100%) in blastn search and 0–0.3% in both p-distance and K2P to a 16S sequence of an unidentified Anguillosyllis specimen (accession number: MK971075 ; ID: Anguillosyllis sp. 43 PB voucher 021-BGR-0045) (see Fig. 7) collected from the BGR contract area of the Eastern CCZ, published in Bonifácio et al. (2020). In terms of the nuclear 18S gene, A. dalgleishae was also well defined, differing from other Anguillosyllis sequences by a minimum of five ( A. cf. hessleri sp. NHM_552 NHMUK2024.1002, A. capensis ZMH _ P25593, A. capensis ZMH _P25594) and a maximum of 16 ( A. capensis ZMH _P25588) mutations (1543 bp sequence).

Remarks

Morphologically, the new species can be distinguished from all other currently known species by the combination of the following characters: body with 10 chaetigers, presence of very large conical dorsal lobes (flaps) in parapodia and presence of dorsal cirri on chaetiger 1 only. Anguillosyllis dalgleishae sp. nov. can be distinguished from seven of the currently known species with 10 chaetigers by the presence of large parapodial dorsal lobes. Such lobes are currently known in only three species, that all possess 11, not 10 chaetigers: A. palpata , A. hampsoni and CCZ species A. truebloodi . Further, SEM confirmed the presence of dorsal cirri on chaetiger 1 only, a character currently confirmed by SEM only in other CCZ specimens assigned to Anguillosyllis cf. hessleri by Drennan et al. (2025). Maciolek (2020) using light microscopy considered such distribution as dorsal cirri “missing” in all but first segments.

0.2

However, given our observations, it may be the case of true absence in the following 10 chaetigers bearing species: A. taleola , A. sepula and A. elegantissima .

Distribution

Eastern CCZ: UK-1 and OMS exploration areas, depth ~ 4200 m. Also, BGR area ( Bonifácio et al. 2020).